Magnetic nanoparticles have potential applications in a variety of next-generation nanotechnology devices, such as high-density magnetic recording media, nanoscale electronics, radio-frequency electromagnetic wave shields, nanocomposite permanent magnets or transformer cores. In the biomedical field, magnetic nanoparticles have potential applications as biomolecule labeling agents or as contrast agents for magnetic resonance imaging (MRI). Nanocomposite permanent magnets having hard magnetic phase nanoparticles and soft magnetic phase nanoparticles may significantly enhance the intrinsic coercivity of permanent magnets, or at least retain desirable energy product values using less quantities of the hard magnetic phase. Accordingly, a reliable supply of hard phase magnetic nanoparticles with desirable size and magnetic properties is required to produce nanocomposite permanent magnets.
In order to fabricate a nanocomposite permanent magnet, it is essential to understand the structure-property relationship of hard phase nanoparticles, which has been severely impeded by the inability to synthesize sub-10 nm sized nanoparticles. Optimization of grain boundaries to achieve spring coupling between soft and hard phase magnetic materials requires the ability to systematically tune nanoparticle size.